1. TECHNICAL FIELD
This invention relates generally to automotive air conditioning control systems, and more particularly, to an automotive air conditioning control system which controls the temperature of the air flow to a passenger compartment by means of an air mix damper driven by a motor actuator for a maximum predetermined period of time.
2. DESCRIPTION OF THE RELEVANT ART
A conventional automotive air conditioning system which includes an automatic air temperature control function is provided with a first control circuit. The first control circuit comprises a microcomputer for computing a desired open angle of an air mix damper in accordance with a preset temperature, an outside air temperature, an inside air temperature and other variable conditions. The control circuit drives the air mix damper to the desired open angle by actuating a drive device, for example, a motor actuator, and thereby controls the temperature of the air flow provided to the passenger compartment.
In the conventional air conditioning system, when a lever or other means for setting the temperature of the air flow to the passenger compartment is positioned at either maximum heating or cooling, the air mix damper is forcedly moved to the position for either maximum heating or cooling, respectively and independently of the variable conditions.
However, when the air mix damper becomes locked due to the introduction of foreign matter or a gear for reducing motor speed of a motor of the motor actuator becomes locked for some reason, the locking may mechanically be transferred to the motor actuator whose motion also becomes locked. If events happen for the worst, the motor of the motor actuator may be destroyed and result in a fire. In order to prevent these problems of the conventional control system, a lock detecting function is included in the first control circuit which cuts off the supply of electricity automatically in accordance with lock detection signals transmitted to the microcomputer of the first control circuit.
However, since the control for the maximum heating or cooling is the responsibility of the second control circuit and not that of the microcomputer, the lock detecting function may fail to operate.